Environmental Engineering Reference
In-Depth Information
Chapter 2
Stormwater Management in Michigan:
Why LID?
Clean water resources are essential to the economic vitality of Michigan. Proper
stormwater management is an essential component of water quality protection.
Low impact development is a cornerstone of stormwater management and thus is
the pathway to protecting water resources and enabling economic growth.
This chapter discusses:
• The importance of the water cycle
• The impacts of stormwater runoff
• An overview of what LID is and how it works
• Benefits of implementing LID
• Cost effectiveness and LID
• Relationship of LID to other programs
• Getting started with LID.
The importance of the water cycle
A key component of protecting water resources is keeping the water cycle
in balance. The movement of rainfall from the atmosphere to the land and
then back to the atmosphere—the water (hydrologic) cycle—is a naturally
continuous process essential to human and virtually all other forms of life
(Figure 2.1). This balanced water cycle of precipitation, evapotranspiration,
infiltration, groundwater recharge, and stream base flow sustains Michigan's
vast but fragile water resources.
In a natural woodland or meadow in Michigan, most of the annual rainfall
soaks into (infiltrates) the soil mantle. Over half of the annual rainfall returns to
the atmosphere through evapotranspiration. Surface vegetation, especially trees,
transpire water to the atmosphere with seasonal variations.
Water that continues to percolate downward through the soil reaches the water
table and moves slowly downgradient under the influence of gravity, ultimately
providing baseflow for streams and rivers, lakes, and wetlands. On an annual
basis, under natural conditions, only a small portion of annual rainfall results in
immediate stormwater runoff (Figure 2.2). Although the total amount of rainfall
varies in different regions of the state (see Chapter 3), the basic relationships of
the water cycle are relatively constant.
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